Data Structures and Algorithms Interview Questions

Discover some of the most common software engineering job interview questions on data structures and algorithms. Use this guide to help you prep!

Data structures and algorithms are a complex part of computer science theory. This is perhaps why they’re a favorite among hiring managers in interview settings for software engineering roles.

This guide features sample interview questions curated from real hiring experiences to better prepare you for your next software engineering interview.

Data structures and algorithms interview questions

Data Structures and Algorithms Interview Questions for Python Users

Python is a versatile and dynamic programming language that is easy for humans to read and write. That makes it a perfect hiring interview language to work with since most interviews will involve many constraints and you’ll have to express your code and logic clearly without any help.

You might have to write down your code on paper, for example, or repeat it vocally over the phone. Python lends itself well to those situations.

Below are some sample Python data structures and algorithms questions you can expect in a software engineering hiring interview.

Question 1: What is the difference between a list and a tuple [in Python]?

Answer: You should know the answer about these default data structures in Python as it’s frequently asked. In short, lists are mutable (they can be modified) while tuples are immutable (they cannot be modified). Lists are ordered by one central index, while a tuple may hold multiple data types together in an index-like-form.

Question 2: Are dictionaries or lists faster for lookups?

Answer: This question tests your grasp of the implications for Python data structures and the algorithms you can implement on top of them. Lists are slower for lookups: it’ll take O(N) time since filtering through for a value will require as a worst-case scenario filtering through every value in the list. Dictionaries are well-set up with key-value pairs, similar to a hash table. Thus the time to search will be O(1) as long as you have the correct key.

Question 3: Show me three different ways of fetching every third item in the list.

Answer: There are three different ways to do this: via a yield function, a list comprehension, or a for loop. All three are demonstrated here.

Question 4: Using list comprehension, print the odd numbers between 0 and 100.

Answer: List comprehensions are a feature in Python that allows us to work with algorithms within the default list data structure in Python. Here, we’re looking for odd numbers.

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A list comprehension allows us to simplify our range and filtering algorithm so we can pack it into one line of code—return every element in the range between 0 and 100, if it divides perfectly by 2.

Be prepared to describe the list comprehension in detail with the right notation if you need to write it down on paper, or recite it over the phone as coding interviews sometimes demand.

Question 5: Write a regular expression that confirms an email id using the python reg expression module “re”?

Answer: This is a tricky one. When it comes to Python algorithms, a lot of the work is usually abstracted away by the built-in default data structures or easy methods that can be called in one line. However, regular expression algorithms, used for filtering through selections of text, are often some of the most difficult to grasp. You’ll have to get familiar with regular expression rules in Python to be able to write out the answer.

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Data Structures and Algorithms Interview Questions for JavaScript Users

JavaScript is not typically taught in universities when data structures and algorithms theory are introduced. Yet, the language powers so much of the modern web today that it’s impossible to ignore.

When going for a software development or web development interview, you might expect the interviewer to test your fundamental knowledge of JavaScript.

Question 1: What is the result of "10"+20+30 in JavaScript?

Answer: This interview question tests your knowledge of JavaScript data primitives, the data types that can be composed into different data structures in Python. In this case, it’s a mix between string and numbers data types. Knowing that the result will be 102030 rather than 60 means that you understand that when a string type is invoked with the + operator in JavaScript, the automatic behavior is to turn it into a concatenation operator.

Only by ensuring that everything that interacts with the + operator is a number or BigInt data type can you ensure that a desired behavior of addition happens.

Question 2: What will be the output of the code below?

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Answer: This question tests your knowledge of arrays and how they interact with different data types. In this case, you should understand that the length of the trees array will still be five even after the delete function. The delete function simply takes the third indexed item (since JavaScript arrays are 0-indexed, this means “maple” or the fourth element) and makes it undefined. The length of the underlying array is still the same, it just contains an undefined element instead of the string “maple”.

Question 3: How do you add an element at the beginning of an array? How do you add one at the end?

Answer: You have to use the default .push() method in order to add something at the end of an array, while you can use the default .unshift() method in order to add something at the beginning. In practice, knowing this answer helps prove that you understand how arrays fundamentally work.

Question 4: What is the for-in loop in JavaScript? Give its syntax.

Answer: This question begins to test your knowledge of algorithms in JavaScript. The for loop is a fundamental part of iterating through data structures. You should be able to describe its syntax to interviewers without hesitation.

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The above is the general case for-loop implementation in JavaScript. You would loop through an array by replacing the object name with the array name, and then place the piece of iterative code inside the block.

Question 5: What are arrow functions?

Answer: Arrow functions are a concise and short way to write functions in ES6 and above. They can be a way for you to condense your algorithmic logic. The example below describes an arrow function which simply prints “hello” in the JavaScript console.

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How Springboard Can Help You Ace Your Software Engineering Interview

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In Springboard’s Software Engineering Career Track, you’ll:

  • Get access to mentors that can help you practice for technical data structures and algorithms interview questions
  • Get personalized career coaching for non-technical interview questions
  • Learn the JavaScript and Python code and frameworks to be able to be very familiar with what hiring managers test for
  • Learn data structures and algorithms across JavaScript and Python

This comes with Springboard's proven approach, which includes:

  • A world-class curriculum built by leading instructor Colt Steele
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Springboard offers a comprehensive software engineering bootcamp. You’ll work with a one-on-one mentor to learn key aspects of front-end web development, back-end web development, databases, and data structures and algorithms. Modules include learning resources, practice exercises, projects, and career-related coursework. 

Check out Springboard's Software Engineering Career Track to see if you qualify.

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Springboard also offers a Software Engineering Prep Course, where you can learn the foundational web development skills (HTML, CSS, and JavaScript) needed to pass the technical skills survey for the Software Engineering Career Track.

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